44 Galls^ Gall-makerSy and Cuckoo Flies. [Sess. 



These curious bunches of crowded twigs are due, as in the 

 case of pollard trees, to the development of numerous axillary 

 buds. When the growth of the terminal bud is arrested, the 

 sap which normally would have gone to nourish it is diverted 

 into buds lower down the stem, which in ordinary course 

 would have remained dormant. The wands used in basket- 

 making are produced by cutting off the upper part of the stem 

 and allowing the axillary buds to develop into rapidly growing 

 shoots. Apparently the destruction of the terminal bud may 

 be effected equally by mites, parasitic fungi, or other agencies^ 



It is unnecessary here to refer to the effects produced on 

 plants by the Uredines and other parasitic leaf-fungi, but 

 mention may be made of the root-tubercles of the bean, birds'- 

 foot trefoil, lupine, hazel, alder, &c., caused by bacteria ; these 

 are by some placed in the category of fungal galls. There is- 

 reason to think, however, that the relation between the twa 

 organisms may be that of partners, of symbiosis rather than 

 parasitism. Even the tubers of the potato have been assigned 

 a similar origin, M. Bernard asserting that they are caused 

 by the attacks of the fungus Fusarium solani. It is pathetic 

 to think that mankind have been eating potatoes all these 

 centuries unconscious of the fact that all along they have been 

 feeding on the galls of a parasitic fungus ! 



One of the most remarkable facts which the study of galls 

 has revealed has now to be stated. All the inmates of a gall 

 do not necessarily belong to the same species. On opening a 

 gall we may find, for example, several orange-coloured cater- 

 pillars of a Cecidomyia, accompanied by several white ones 

 belonging to a different insect altogether, as occasionally 

 happens in the reddish woolly galls of C. veronicas on the 

 speedwell. A section of the marble gall-nut shows very often 

 not only the central cavity containing the larva of Cynips 

 Kollari, but also several smaller cavities nearer the surface in- 

 habited by Cecidomyias or other species of Cynips. The pea- 

 shaped gall on the wild brier normally has but a single central 

 chamber occupied by Ehodites eglanteriae, but very often this 

 is surrounded by smaller cells containing the larvse of Peri- 

 clistus caninge. Besides the larvae of Biorhiza aptera, its 

 legitimate owners, the oak-apple usually contains numerous 

 guests, including the caterpillars of several moths. One of 



